The present invention relates to improvements in a deflection yoke for deflecting an electron beam electromagnetically when a high energy electron beam is used in a cathode ray tube (referred to as CRT hereafter).
FIGS. 7 through 9 are rear elevations showing a prior art yoke seen from the rear of the CRT. An annular core 1 substantially cylindrical in shape surrounds an electron-gun portion at the rear of the CRT and is mounted around an outer circumference of a small-diameter portion of the CRT.
A pair of horizontal coils 2 and 3 are first coils disposed substantially horizontally along the inner circumferential surface of the annular core 1.
Vertical coils 4 and 5 are second coils formed by a conductor wire wound directly around the core 1 in a so-called "torodial-winding" using a special coil-winding machine (not shown diagrammatically).
The operation of a deflection yoke in the above arrangement is described as follows:
A horizontal magnetic flux 6 is generated by coils 2 and 3 in a direction of solid arrows as shown in FIG. 7 and a vertical magnetic flux 7 is generated by vertical coils 4 and 5 in the direction of the solid arrows as shown in FIG. 8. A magnetic field having the flux oriented in these two directions is set up in such a way that the annular core is positioned at a center of the magnetic field.
The magnetic field intensity of the horizontal magnetic flux 6 and vertical magnetic flux 7 vary in response to the amount of current through the horizontal coils 2 and 3 and the vertical coils 4 and 5, respectively. The directions of the flux alternate from the directions in solid arrows 6 and 7 to the directions in dotted arrows 6' and 7', respectively in response to the direction of the current.
The direction of an electron beam passing through the small-diameter portion of the CRT which is inserted into the annular core is deflected by the magnetic field and an image is displayed brightly on the CRT.
Since the horizontal magnetic flux 6 passes through two semi-circular magnetic paths passing through the annular core 1 as shown in FIG. 9, it causes opposing magnetic poles 1a and 1b to set up at the upper part and the lower part of the annular core 1 respectively.
The polarities of these magnetic poles change from N to S and back to N in alternating fashion and therefore an alternating magnetic field is formed in such a way that the annular core 1 is positioned at a center of the alternating magnetic field. A leakage flux 8 which is emitted from the yoke outwardly is produced between the poles 1a and 1b.